Granulocyte transfusion support of patients with granulocytopenia and/or granulocyte dysfunction has recently reemerged as a therapeutic blood product because of the discovery that normal donors pretreated with Granulocyte- Colony Stimulating Factor (G-CSF) with or without oral dexamethasone release high concentrations of granulocytes into the peripheral circulation within 24 hours after G-CSF administration. The collection of high concentrations of G-CSF primed granulocytes with leukapheresis procedures is facilitating an increased use of this unlicensed product. Several questions that need to be addressed include the long term safety of normal donors receiving G-CSF, the functional properties of the granulocyte product, and the appropriate storage conditions of the product prior to transfusion. In a collaboration with the NIH Clinical Center Department of Transfusion Medicine, we are evaluating the cellular activation and functional properties of the product and our NIH colleagues are monitoring the hematologic and clinical status of the normal donors. Normal donors are randomized to receive one of three different mobilization regimens of: 1) oral dexamethasone alone, 2) G-CSF alone, or 3) a combination of dexamethasone and G-CSF. Each normal donor will undergo all mobilization regimens with a wash-out period of at least 3 weeks between product collections. Granulocyte products usually contain 10-fold or greater excess of platelets in the final product and G-CSF appears to stimulate platelet and granulocyte function. We are evaluating the interaction of platelets and granulocytes in the product using flow cytometric techniques to quantify the number of platelets adherent to granulocytes and the expression of a variety of activation and adhesion molecules on platelets and granulocytes otbained in normal donors: 1) prior to drug administration, 2) in the collected granulocyte transfusion product immediately after apheresis, and 3) in the collected product stored overnight in a blood bank setting. Granulocyte function, assessed by chemotactic responsiveness to two different chemoattractants, is evaluated on the freshly collected products and products that have been stored overnight. Products collected from nine different donors indicate that less than 10% of baseline granulocytes (collected prior to drug treatment of donor)have platelets adherent to them; however, 53+/-9% (mean +/- SEM)of the apheresis granulocyte product (collected 24 hours after drug administration) have platelets adherent to them and storage of the product overnight results in an increase to 76+/-8% of the granulocytes with adherent platelets. Platelets adhered to baseline granulocytes do not express the platelet activation protein P-selectin, whereas, 17+/-5% of platelets adherent to apheresis product express P-selectin, and storage overnight results in 67+/-7% of platelets expressing P-selectin. Granulocyte products have normal chemotactic activity, however, when stored overnight, products have a variable loss in chemotactic responsiveness.